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c61c6d9880
Signed-off-by: Peter S. Mazinger <ps.m@gmx.net> Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
93 lines
2.3 KiB
C
93 lines
2.3 KiB
C
/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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* rint(x)
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* Return x rounded to integral value according to the prevailing
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* rounding mode.
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* Method:
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* Using floating addition.
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* Exception:
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* Inexact flag raised if x not equal to rint(x).
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*/
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#include "math.h"
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#include "math_private.h"
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static const double
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TWO52[2]={
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4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
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-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
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};
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double rint(double x)
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{
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int32_t i0, _j0, sx;
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u_int32_t i,i1;
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double t;
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/* We use w = x + 2^52; t = w - 2^52; trick to round x to integer.
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* This trick requires that compiler does not optimize it
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* by keeping intermediate result w in a register wider than double.
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* Declaring w volatile assures that value gets truncated to double
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* (unfortunately, it also forces store+load):
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*/
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volatile double w;
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EXTRACT_WORDS(i0,i1,x);
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/* Unbiased exponent */
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_j0 = ((((u_int32_t)i0) >> 20)&0x7ff)-0x3ff;
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if (_j0 > 51) {
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//Why bother? Just returning x works too
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//if (_j0 == 0x400) /* inf or NaN */
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// return x+x;
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return x; /* x is integral */
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}
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/* Sign */
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sx = ((u_int32_t)i0) >> 31;
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if (_j0<20) {
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if (_j0<0) { /* |x| < 1 */
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if (((i0&0x7fffffff)|i1)==0) return x;
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i1 |= (i0&0x0fffff);
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i0 &= 0xfffe0000;
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i0 |= ((i1|-i1)>>12)&0x80000;
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SET_HIGH_WORD(x,i0);
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w = TWO52[sx]+x;
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t = w-TWO52[sx];
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GET_HIGH_WORD(i0,t);
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SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
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return t;
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} else {
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i = (0x000fffff)>>_j0;
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if (((i0&i)|i1)==0) return x; /* x is integral */
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i>>=1;
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if (((i0&i)|i1)!=0) {
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if (_j0==19) i1 = 0x40000000;
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else i0 = (i0&(~i))|((0x20000)>>_j0);
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}
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}
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} else {
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i = ((u_int32_t)(0xffffffff))>>(_j0-20);
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if ((i1&i)==0) return x; /* x is integral */
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i>>=1;
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if ((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(_j0-20));
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}
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INSERT_WORDS(x,i0,i1);
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w = TWO52[sx]+x;
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return w-TWO52[sx];
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}
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libm_hidden_def(rint)
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strong_alias(rint, nearbyint)
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libm_hidden_def(nearbyint)
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